space physics

Created by: sophiiealiice
Created on: 15-04-19 17:38

View mindmap

space physics
- the life cycle of stars
  - nebula - cloud of dust and gas
    - the force of gravity pulls it together to form a...
      - protostar
        as the star gets denser, the temperature rises and more particles collide with each other
        when the temperature gets high enough, hydrogen nuclei undergo nuclear fusion to form helium nuclei
        this gives out huge amounts of energy, which keeps the core of the star hot. a star is born
        main sequence star
        the star enters a long stable period, outward pressure caused by the nuclear fusion (trying to expand the star) balances the force of gravity (pulling everything inwards)
        
        typically lasts several billion years
        
        eventually, hydrogen begins to run out and the star swells into
        red super giant
        if it was larger star
        
        it becomes red because the surface cools.
        
        fusion of helium and other elements occurs. heavier elements (e.g. Fe) are created in the core of the star
        
        it starts to glow brightly again, as it undergoes more fusion and expands and contracts several times, forming elements as heavy as iron
        eventually they explode into a
        supernova
        forming elements heavier than iron and ejecting them into the universe to form new planets and stars
        
        this throws the outer layers of dust and gas into space, leaving a very dense core called a
        neutron star
        
        if the star is massive enough, it will become a
        black hole
        a super dense point in space that not even light can escape from
        
        red giant
        if its was small star
        
        it becomes red because the surface cools.
        
        fusion of helium and other elements occurs. heavier elements (e.g. Fe) are created in the core of the star
        
        it becomes unstable and ejects its outer layer of dust and gas
        this leaves behind a hot, dense, solid core - a
        white dwarf
        as this cools down, it emits less and less energy
        when it no longer emits a significant amount of energy it is called a
        black dwarf
  - stars and their life cycles produce and distribute all naturally occurring elements
- the solar system
  - the sun is the centre of our solar system. it is orbited by:
    - planets
      - large objects that orbit a star
      - 8 in our solar system
      - must be large enough to have "cleared their neighbourhoods"
        meaning their gravity must be strong enough to have pulled in any nearby objects apart from their satellites
    - moons
      - orbit planets
      - a type of natural satelilte
    - dwarf planets
      - e.g. pluto
      - planet like objects that orbit stars but don't meet all the rules for being a planet
    - artificial satellites
      - satellites built by humans
      - generally orbit earth
  - part of the milky way - a massive collection of billions of stars that are all held together by gravity
  - satellite - an object that orbits a second, more massive object
- orbits
  - the size of the orbit depends on the object's speed
    - the closer you get to a star or a planet, the stronger the gravitational force is
    - the stronger the force, the faster the orbiting object needs to travel to remain in orbit
      - to not crash into the object that it's orbiting
    - for an object in stable orbit, if the speed of the object changes, the radius of its orbit must do so too.
      - faster moving objects will move in a stable orbit with a smaller radius than slower moving ones
  - gravity provides the force that creates orbits
    - the planets orbit around the sun in almost circular orbits
      - the same goes for the moon around the earth
      - if an object is travelling in a circle, it is constantly changing direction
        so it is constantly accelerating
        
        so it is constantly changing velocity (but NOT speed)
        
        for an object to accelerate, there must be a force acting on it
        this force is directed towards the centre of the circle
        
        this force would cause the object to just fall towards whatever it was orbiting
        but as the object is already moving, it just causes it to change direction
        
        the object keeps accelerating towards what it's orbiting but the instantaneous velocity (right angles to the acceleration) keeps it travelling in a circle
        the force that makes this happen is provided by the gravitational force between the planet and the sun
        or between the planet and its satellites
- red shift and the big bang
  - the universe seems to be expanding
    - this evidence suggests the universe started with a bang
      - new evidence might change theories
        big bang is the best guess so far
        
        whenever scientists discover new evidence, they either have to make a new theory or change a current on to explain what they've observed
        
        there is still lots that scientists don't know about the universe
        
        observations of supernovae from 1998 to the present day appear to show that distant galaxies are receding at an increasing speed
        
        currently, scientists think that the universe is mostly made up of dark matter and dark energy
        dark matter is the name given to an unknown substance which holds galaxies together but does not emit any electromagnetic radiation
        
        dark energy is thought to be responsible for the accelerated expansion of the universe
        
        no one really knows what dark matter and dark energy are so there are lots of different theories about it
        these theories get tested over time and are either accepted or rejected.
      - something must have made the universe expanding
      - initially all the matter in the universe occupied a very small space. this tiny space was very dense and so was very hot
      - then it 'exploded' - space started expanding, and the expansion is still going on
    - when we look at light from most distant galaxies, the wavelength has increased
      - the wavelengths are all longer than they should be - they're shifted towards the red end of the spectrum. this is called red shift
        this suggests that the source of the light is moving away from us
        measurements of the red-shift indicate that these distant galaxies are moving away from us (receding) very quickly - and it's the same result whichever way you look
        more distant galaxies have greater red shifts than nearer ones - and so all galaxies are moving away from every other galaxy, not just ours
        the conclusion appears to be that the whole universe is expanding
    - analogy
      - a ballon covered with pompoms
        as the balloon is inflated, it stretches
        the pompoms mover further away from each other
        the ballon represents the universe and each pompom is a galaxy
        as time goes on, space stretches and expands, moving the galaxies away from each other
        this is a simple model
        but it shows how the expansion of space makes it look like galaxies are moving away from us
        
        balloons only stretch so far
        
        there would be galaxies inside the balloon too

Get Revising

space physics

Comments

Similar Physics resources: